Enraged Jaguars, violent winds of hurricane force, and a mysterious "giant" who roams the jungle around the Mayan village in Yucatan, Mexico, where Tom is encamped, are only a few of the perils that the young inventor encounters during his thrilling expedition.

But even more feared by the young inventor is an unknown saboteur, intent on destroying Tom's two latest inventions--the electronic retroscope camera and his "parachute" plane, designed for landing in small areas.

Undaunted by the hazards that surround him and assisted by teh friendly natives, Tom perseveres in his objectives. He tests his paraplane for landing maneuverability in densely grown jungle areas, and uses his retroscope (magic to the natives!) to restore--photographically--ancient carvings and writing on old Mayan relics. Tom is astounded when he discovers that some of the carved symbols are similar to the mathematical symbols used by his mysterious friends in outer space to communicate with him.

Is it possible, Tom wonders, that beings from another planet actually landed in Yucatan centuries ago?

What happens to Tom and his friends as they seek the answer to this question in the dark depths of a buried temple will hold every reader in gripping suspense to the last line of this challenging adventure.

The summary below was written by Graeme Woods. Thanks for volunteering!

Major Inventions: The Electronic Retroscope

The

Electronic Retroscope is the major invention of this book.

What does the Electronic Retroscope do?

The Retroscope is a television like camera that allows one to see what an old, worn object used to look like. For example, Tom used it to photograph a worn stone carving to read the original inscriptions. The book describes it as follows:

Tomís latest invention was designed to "see" what a rock face ñ or any other surface ñ looked like originally, before being exposed to wear or erosion. Tom believed that it would prove highly useful in scientific research by geologists, archaeologists, and paleontologists.

Tom explains that the name of his invention is formed from Greek and Latin words meaning "to see back".

How does the Electronic Retroscope work?

The book is initially a bit vague about the operating principles of the Retroscope. It says:

The camera was based on two earlier achievements of the Swifts. One was Tomís discovery of a hitherto unknown electromagnetic radiation given off by all matter. This had led to the invention of the Swift spectroscope and the force-ray repeletron used in Tomís latest spaceship.

The new camera also made use of certain detector features invented by Mr. Swift and used in Tomís "Eye-Spy" camera which could take motion pictures through a wall or other solid object.

The retroscope is described as being in three parts; the camera, an "electronic brain" and a reproducing unit consisting of a cathode ray tube and a photographic output system.

This is how Tom explains the operation of the camera:

"It looks complicated, but the basic principle is fairly simple," Tom said. "As you know, any rock may undergo radioactive aging as its natural elements break down and become other elements. That happens all through the rock. But the layers nearer the surface are more exposed to cosmic radiation from the outside."

"Your dad said that youíre interested in studying some rock carvings," put in Jack. "A carved surface means that different layers of rock are exposed all at one time."

"Exactly," said Tom. "For instance, if you carve a gouge in the rock, the cosmic radiation would penetrate deeper at that point than it would in an uncarved part of the rock. Therefore, the radioactivity inside the rock follows the same in-and-out depth pattern as the carving on the rockís surface."

"Wait a minute!" Dick snapped his fingers. "I think I get it. By measuring the radioactivity all through the rock, you can figure out what the carving looked like before it was worn away!"

"Right," Tom said. "Now my camera here has two detectors. One scans the whole surface of the rock to probe out differences in radioactivity; the other stays focussed on one unworn spot on the rock surface to show the basic level of the rockís radioactive aging."

Tom has to redesign his camera when he finds that the pictures are unclear due to external radiation, such as cosmic rays. Eventually he uses some radiation screening devices in conjunction with the electronic brain to cancel out the radiation. The books explains it like this:

Actually two fields would be necessary, he soon realized ñ one above the camera detectors and one below. Any radiation that passed through both fields would automatically "identify itself" as coming from the upper atmosphere. The electronic brain could be "ordered" to throw out such radiation.

On the other hand, all radiation coming from the object being photographed would pass between the two fields. The brain would use only this radiation in making its computations and thus produce a clear picture without interference.

Would the Retroscope work?

As I understand it from the book, the retroscope works by bombarding an object with radiation then measuring the radiation that comes back from each point of the object against the average level inside. The average level of radiation inside the object is assumed to be purely the result of natural radioactive decay (all rocks contain a small amount of radioactive isotopes that slowly decay into other elements).

Cosmic radiation would cause changes in the objectís composition at a constant level under the original carving. The retroscope would measure this against the background radiation of the object to determine the original appearance.

The feasibility of this invention rests on whether cosmic rays change a material that they hit. Cosmic rays are high-energy particles from space that constantly bombard the earth from every direction. About 87% of cosmic rays are protons and about 12% are alpha particles. These types of particles should change an object that they hit in some way. The difficulty is measuring this, but I believe the invention could be made to work.

This invention reminds me of carbon dating, but it is non-destructive and works for inorganic objects.

The statement about the retroscope using the discovery of the previously unknown form of electromagnetic radiation used for the repeletron seems to be at odds with the explanations elsewhere in the book, unless the radiation is used in the scanning process.

It is interesting that Tom uses an electronic brain to process the information. This is described in other books as a programmable analog computer. This would be the best way to manage the detailed calculations needed to reconstruct the original appearance of an object from a three-dimensional scan. The benefit of an analog computer over the digital computers of the day was in their compactness and high speed.

What impact would the retroscope have on our lives?

I believe that the retroscope would useful for archeological work and would have very limited application in other areas.

The Paraplane

The

paraplane is the other significant invention in this book.

How does the paraplane work?

The paraplane is a small jet aircraft that also has a dirigible bag that can be used to provide buoyancy when the jet motor is not used. Here is a description from the book that explains the principle of the paraplane:

The plane was part jet plane and part dirigible. After the dirigibleís bag was filled with helium, so the plane could float without power, the bag could then be slowly deflated to bring the ship gently to earth.

The paraplane is stored on board the Flying Lab with its wings folded into the fuselage. The wings deploy shortly after it is launched. Although it is small, it is has enough cabin space to accommodate Tom, Bud and Chow on its first flight in Mexico and later in the book it carries Tom and three police officers.

The dirigible bag is only filled with helium when needed, as the idea is that it is for emergency use or for take-off and landing in tight spots. This is how Tom explains the operation to Chow in the test flight:

"How we goiní to float down in this contraption"? Chow eyed the strange-looking craft uneasily. "I thought it was síposed to have some kind oí balloon or somethiní."

"It has," Tom replied, "but the dirigible bag is deflated now and stowed inside this pod." He pointed to a domelike bulge on top of the fuselage. "Weíll blow it up with helium as soon as weíre air-borne."

To descend to earth, the process is reversed. This is how the book explains it:

The helium tanks were mounted in a small compartment at the rear of the cabin. Tom switched on an electric pump and compressor to suck the helium back into the tanks. A humming sound filled the plane as the bag deflated. Gently the paraplane descended towards the treetops.

Would the paraplane work?

The paraplane could work, but there are some practical issues to work out before it could work as described.

The book doesnít give any indication of how big the dirigible is but a fairly large dirigible would be needed to provide adequate lifting force to overcome the weight of an aircraft and its passengers, even a small, light one like the paraplane. Even if the paraplane was extremely light, the weight of four passengers on board would represent at least 350 kg. Also, there is the weight of the helium tanks, compressor and fuel to take into account although the dirigible envelope itself would be fairly light.

Goodyear developed a heavy lifting balloon for logging and this comprised two balloons, each 110 feet long and 28 feet in diameter, with 75,000 cubic feet of helium. This could lift several tons. A balloon to lift cargo from Navy ships had a capacity of 530,000 cubic feet. Whilst the paraplane dirigible wouldnít need to lift anywhere near this weight, it gives an idea of the size of the dirigible envelope required to lift a substantial weight. Also a large volume of helium would have to be stored in the tanks, meaning that the tanks would be large and heavy.

The dirigibleís envelope could be easily stored as described in the book. In fact, the Echo series of balloon space satellites were stored ready for deployment in a 26-inch diameter container and opened up to be 100 feet in diameter.

Also, the mid-air inflation would be possible and this has actually been done in a technique developed by the U.S. National Bureau of Standards, Boulder, Colorado. The technique does not use pressurized helium as with Tomís paraplane. The helium is stored as a liquid (which is more compact) and converted to gas with a special heater. Mid air inflation takes about 5 minutes and the platform is launched from an airplane and supported by a parachute whilst inflating.

I do have some doubts about a small electric compressor being able to deflate the balloon. I think that a compressor that could deflate a large balloon and put the helium back into high pressure tanks would need a lot of energy, and it would not be a quick process as with the paraplane.

What impact would a paraplane have on our lives?

A paraplane would offer a number of benefits. It would be able to take off or land in very confined spaces with the help of the dirigible. Virtually any open space could serve as an airfield, without the need to build expensive runways.

Also in an emergency, the dirigible could provide a soft landing, saving lives.

Recently work has been done on parachutes that can provide a soft landing for light aircraft, but unfortunately these are not yet widely used.

Until the practical issues associated with the paraplane idea are sorted out, it is unlikely that we will see one in operation.